Correction of errors occurring in electronic timepieces

ABSTRACT

The indicator gear train of a timepiece is driven in dependence upon periodic signals derived from a time base. The gear train includes a rotatable element which can periodically separate the electrodes of a variable capacitor comprising two electrodes biased one against the other with the interposition between them of a dielectric layer. An error detector circuit can be used to detect errors in the gear train position by comparing signals derived from the time base with signals dependent upon the value of the variable capacitor.

United States Patent Diime Feb. 5, 1974 [54] CORRECTION OF ERRORS OCCURRING IN 3,451,210 6/1969 Helterline et al. 58/28 R ELE O TIMEPIECES 3,553,957 1/1971 Dome et a1. 58/23 A 3,609,957 10/1971 Emerson et a1. 58/23 R Inventor: Peter Dome, gg Bel Blel, 3,564,838 2/1971 Fellrath a a1. 53/23 A Switzerland [73] Assignee: Societe Suisse Pour Llndustrie Examiner-Richard Wilkinson B -l SA, Geneva, Switzerland Assistant ExaminerEdith Simmons Jackmon Attorney, Agent, or FirmEric H. Waters et a1. [22] F1led: Oct. 20, 1972 [21] Appl. No.: 299,327 57 ABSTRACT The indicator gear train of a timepiece is driven in de- [30] Foreign Application Priority Data pendence upon periodic signals derived from a time Oct. 25, 1971 Switzerland 15484/71 base- The gear train ineludes a rotatable element which can periodically separate the electrodes of a 52 US. Cl 58/23 R, 58/34, 318/662 variable capacitor comprising twe electrodes biased 51 Int. Cl G04c 3/00 one against the other with the interposition between [58] Field of Search 58/23 A, 23 R, 34, 35 R; them of a dielectric layer. An error detector circuit 31 2 can be used to detect errors in the gear train position by comparing signals derived from the time base with [56] References Ci d signals dependent upon the value of the variable ca- UNITED STATES PATENTS 1,928,793 10/1933 Poole 58/35 R 17 Claims, 5 Drawing Figures D I VI 0 E R 5 E020 EC2| EC 22 EC 23 C20 .1 Li T24 C40 P PATENTED 51574 3,789,599

SHEET 1 BF 2 DIVIDERS A 7 FIG. 2 EC2O E62! EC22 EC23 020 021 0&3

PATENTED 5974 3,789,599

SHEET 2 BF 2 DIVIDERS ECZO EC2| EC22 EC23 A C4 (P FIG. 5

CORRECTION OF ERRORS OCCURRING IN ELECTRONIC TIMEPIECES BACKGROUND OF THE INVENTlON British Pat. No. 1,177,523 discloses an electronic timepiece comprising a time base supplying high frequency electrical signals, an electronic divider of this frequency constituted by a series of divider stages, and an hour indication device which comprises means for indicating the hour and which is controlled by the demultiplied frequency signals issuing from the demultiplier.

The disclosed timepiece is provided with a correction device comprising means for periodically detecting any deviation in the position of the hour indicating means relative to a reference position corresponding to that position which the hour indicating means are required to occupy at the instant of detection on the basis of the counting of the signals issuing from the divider. The timepiece also includes means for forming a signal for discriminating the direction of the said positional deviation of the hour indicating means, means for momentarily connecting the hour indicating device to an intermediate stage of the divider, when the said discrimination signal corresponds to a delay in the hour indicating means, in such manner as to accelerate the operation of the said device in order to make up for the said delay, and means for momentarily interrupting any connection between the divider and the hour indicating means, when the discrimination signal corresponds to an advance of the hour indicating means, in such manner as to cancel the said advance by stopping the said device.

The detection means of the correction device described in the aforementioned British Pat. No. 1,177,523 are constituted by a variable capacitor which takes the form of a rotary support which is connected to the hour indicating means and which is designed to effect an angular displacement through 180 in the period of time separating two successive control signals, whereas hour indication corresponds to that which it should in fact be on the basis of the divided frequency signals issuing from the divider. The said rotary support comprises two diametrically opposed electrodes which are displaced opposite two fixed electrodes provided for scanning the rotary support electrodes. The said fixed electrodes each extend along a portion of the circular path followed by the electrodes of the rotary support, each along a travel path corresponding to at least two successive intermittent displacements of the electrodes of the rotary support and in a relative position such that they are diametrically opposed at one of their ends and are directed in angularly opposite directions from that end. The rotary support is angularly positioned in such manner that, when it rotates, its electrodes each pass into position opposite an associated fixed electrode when they receive the control signal and that the indication of the hour corresponds to that which it should in fact be on the basis of the counting of the signals which are issued from the divider. Any other position of the electrodes of the rotary support relative to the fixed electrodes at the instant at which they receive the control signal signifies that the indication is incorrect.

in a wristlet watch, the space available for a variable detection capacitor is of the order'of a few millimetres. In view of the fact that, in the example described in British Pat. No. 1,177,523, the mobile support effects one revolution every 64 seconds, the angular extent of the fixed electrodes is very reduced.

Furthermore, there must be a clearance between the fixed and the mobile electrodes in order that the latter may rotate freely without friction against the fixed electrode.

It is a result of these two factors that the ratio between the detectable capacity variation in two successive angular positions of the mobile electrode and the parasite capacity of the circuit is relatively small.

It is the object of the present invention to remedy these disadvantages.

DISCUSSION OF THE DISCLOSURE According to one aspect of the present invention there is provided a timepiece indicator gear train having a rotatable element and means for sensing the angular position of said element, said means comprising:

relatively movable electrode surfaces which have a first relative position in which a movable one of said surfaces lies against another of said surfaces;

a dielectric layer provided on at least one of said one and said another surface;

biasing means which urge said electrode surfaces to said first relative position;

a coupling portion of said gear train; and g a coupling portion of said one of said electrode surfaces for co-operation with said coupling portion of said gear train to cause said electrode surfaces to be periodically moved apart against the action of said biasing means during rotation of said element of said gear train.

According to a further aspect of the invention there is provided an electronic timepiece comprising:

the timepiece indicator gear train defined above;

electrically operable drive means coupled to said gear train;

a timebase coupled to said drive means to operate said drive means in dependence upon periodic signals issued by said timebase at a predetermined frequency; and

an error detection circuit coupled to said means for sensing the angular position of said element and also to said timebase, said error detector circuit being operable to detect error in the angular position of said element in dependence upon a comparison between signals from said timebase and from said means for sensing the angular position of said element.

The fact that the electrode surfaces may be applied against each other with interpositioning of the dielectric layer has the result that it makes it possible to obtain a particularly high capacity between these surfaces. Furthermore, the capacity between the surfaces varies suddenly as soon as the electrode surfaces are separated to a small extent, so that the arrangement has been found to be particularly suitable for industrial utilisation within the framework of a correction device such as that disclosed in British Pat. No. 1,177,523.

BRIEF DESCRlPTlON OF THE DRAWINGS For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:

FIG. 1 is a plan view of an error detector of a gear train;

FIG. 2 is a diagram of a first error detector and corrector circuit in conjunction with the variable capacitor of FIG. 1;

FIG. 3 is a diagram of a second error detector and corrector circuit;

FIG. 4 shows explanatory waveform diagrams; and

FIG. 5 is a diagram showing the possible variation of the capacity of the variable capacitor shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS The timepiece indicator gear train a portion of which is shown in FIG. 1 is intended to be mounted in an electronic timepiece, for example a timepiece of the type described and illustrated in British Pat. No. 1,177,523. Thus, the following text will be restricted to a description of the constructional features of the gear train and of the circuits with which the said gear train is connected.

The gear train comprises (FIG. 1) an element constituted by a disc 1 which is provided, at its periphery, with eight projections in the form of stops or lugs 2 and which is secured on the arbor 3 of an escape wheel (not shown) of the gear train driven step-by-step in rotation Y in the direction of the arrow F, at a rate of, for example,

one revolution every 32 seconds.

A variable detector capacitor C4 is mounted on the housing (not shown) of the timepiece, near the disc I. The said capacitor comprises a pivotable electrode 5 secured to a shaft 6 mounted for pivoting in the frame or housing, parallel to the arbor 3 of the disc 1. The electrode 5 has six radially extending arms or vanes enclosing equal angles. The surface of the electrode 5, which is made preferably from aluminium, is covered with an insulating layer of aluminium oxide which has been produced by any known means and the thickness of which is of the order of a few microns. This layer constitutes the dielectric of the capacitor in the position wherein the electrode surfaces thereof (provided by'the vanes) are close together, as will be discussed later in this text. The dielectric could also be formed by a layer of some other insulating material.

The fixed electrode of the variable capacitor C4 is constituted by a disc 7 fixed to the frame or casing (not shown) of the timepiece and provided with six vanes 7a uniformly distributed about the pivoting arbor 6 of the electrode 5. Each vane 7a extends parallel to a diametral plane extending through the axis of the arbor 6, each vane 7a extending at a distance from the corresponding diametral plane equal to half the thickness of an arm of the mobile electrode 5. Consequently, when the electrode 5 occupies the angular position shown in full lines in FIG. 1, one face of each of the arms of the electrode 5 contacts one face of an associated vane 7a. Fast on the arbor 6 is an end piece or ferrule 8 serving for securing the inner end of a spiral recoil spring S the outer end of which is secured to the frame or housing of the timepiece by an eye-bolt 10 constituting the terminal of the electrode 5 of the variable capacitor (FIGS. 2 and 3). The spring S is wound-up slightly to act as resilient biasing means urging the arms of the electrode 5 against the vanes 70 of the fixed armature 7.

A lever 11, acting as an entrainment finger, is secured on the arbor 6 and extends radially towards the disc 1, in substantially coplanar position relative to the latter. Furthermore, the free end of the lever 11 intersects the circular trajectory described by the respective ends of the stops 2 on the disc 1 in the two angular positions shown in FIG. I. These two positions correspond to two successive positions of the escape wheel driven step-by-step and on the arbor 3 on which the disc 1 is secured. As FIG. 1 shows, the free end of the arm 11 is entrained by a stop 2 during an angular displacement of the stop which is slightly larger than one step of the escape wheel, in such manner that, since the indication or display repetition period is one second in the example considered, the electrode 5 will remain spaced away from the vanes 7a of the fixed electrode for a time duration corresponding to that period.

The time interval separating two successive detection operations is dependent on the number e of the stops 2 on the disc 1, on the number Z of teeth on the seconds wheel of the gear train and on the period T of entrainment of the indicating means of the timepiece. The dependency is such that the time interval referred to equals In the illustrated embodiment, the period T has been selected to be equal to 1 second. In this time interval, the electrode 5 thus travels away once from the vanes 7a of the fixed armature. The detection capacitor C4 may be connected either in the circuit shown in FIG. 2, which is designed to permit delay correction, or in the circuit of FIG. 3 which is intended to effect advance corrections.

FIG. 2 shows only the two last stages-EC 20 and EC 21 of an electronic divider for the signals issuing from the time base of the electronic timepiece. The timebase may be constituted by a quartz oscillator, notably one of extremely high frequency. Following on these two stages, the electronic circuit has two auxiliary divider stages EC 22 and EC 23.

The signal issuing from stage EC 20 has a frequency of 2 cycles per second, whereas the frequency of that emanating from the following stage, EC 21, is 1 cycle per second. Since the divider stages EC 22 and EC 23 are stages capable of dividing by 2, the frequency applied to them or, respectively, the signal issuing from stage EC 23 has a frequency of one-fourth cycle per second.

Since the disc 1 is driven at the velocity of l revolution every 32 seconds, and since the disc 1 comprises eight stops 2, it follows that the disc 1 triggers the periodic rocking of the lever 11, out of the position shown in full lines (FIG. 1) into the position shown in broken lines, once every 4 seconds.

Furthermore, since the displacement of the disc 1 corresponds to that of the escape wheel, and since the escape wheel is driven one step per second, it follows that, if operation of the timepiece is correct, i.e., if the hour indication corresponds effectively to a counting of all the pulses emanating from the timebase, then a signal leaving the stage EC 23 will be produced at an instant at which the electrode 5 of the capacitor C4 is spaced away from the fixed electrode. The benefits resulting from such synchronism will be illustrated hereinbelow.

Before continuing the description of the circuit shown in FIG. 2, it should be mentioned that all the transistors utilised in the circuit (and also in the circuit of FIG. 3) are field effect transistors having an insulated control electrode of the type known as isolated gate field effect transistors.

The correction circuit shown in FIG. 2 comprises a circuit R6, T26, C16, T24, T23 for driving an electromechanical converter (not shown) of the timepiece, the said converters being in every respect identical with those shown in FIG. 8 of British Pat. No. 1,177,523 for example. Reference should be made to this specification if more details are required. As shown in the drawing, the electrode for controlling the transistor T23 is connected to output b of the divider stage EC 20, whereas that of the transistor T24 is connected to output a21 of the stage EC 21. A transistor T is connected in parallel with the capacitor C16 between the negative pole of a dc. source P and the input of the transistor T26. The circuit comprises furthermore a transistor T27 connected in series on the one hand to the electrode for controlling the transistor T27 and on the other hand to a capacitor C17 across'the output a20 of the stage EC 20. The electrode for controlling the transistor T27 is connected to the terminal 10 of the electrode 5 of the variable capacitor C4. The control electrode of transistor T27 is also connected to one of the electrodes of an fixed capacitor C40.

The circuit also comprises a transistor T29 connected, via a capacitor C18 to the negative pole of the dc. source P, the transistor T29 being furthermore connected at point 9 to the second electrode of the unvariable capacitor C40. The transistor T28 is connected between the negative pole of the source P and a point 0 to which are connected the capacitor C18 and the transistor T29. The control electrode for the transistor T28 is connected to the output 023 of the divider stage EC 23.

A capacitor C19 is connected between the negative pole of the source P and the control electrode for the transistor T29. Furthermore, two transistors T and T31 are connected in series across the source P, the output of the transistor T31 being connected to the electrode for controlling the transistor T29. Finally, the circuit comprises a transistor T32 connected in series with a capacitor C20 across the output a21 of the divider stage EC 21, the output of the transistor T32 being connected to the electrode for controlling the transistor T30, whereas the electrodes for controlling the transistors T31 and T32 are connected in common to the output a23 of the divider stage EC 23.

Control of the position of the gear train is effected by a signal V9 which is taken off at point 0 in the circuit (FIG. 2) and applied to the capacitor C40. The duration of this signal determines the period of error detection and correction.

The manner in which the said signal V9 is obtained will now be discussed and for that purpose it will be assumed that, at the instant at which the signals Va21 and Va23 are simultaneously emitted by the respective demultiplier stages (FIG. 4) the capacitor C18 is charged, the capacitor C19 is discharged, and the transistor T29 is conductive, so that that electrode of the capacitor C40 which is connected to the point 9 is at zero potential (V9 0) and the transistors T28, T30, T31 and T32 are blocked.

Before continuing this explanation and in order that the diagram of FIG. 4 may be well understood, it should be recalled that, in the illustrated example, the divider stages are of the type illustrated in F IG. 7 of British Pat.

No. 1,177,523. Thus, Vg' represents the voltage in the general feed line (not shown) of the stages EC of the divider, Vb20 represents a voltage taken off at a point b20 on the circuit of stage EC 20, and Vm represents the voltage at point m.

At the instant at which the signal Va23, synchronised with the signal Va21, appears the transistors T28, T30, T31 and T32 become conductive, in such manner that:

l. The capacitor C18 is discharged, this bringing the points 0 and 9 to the negative potential of the source P (formation of the pulse front V9 FIG. 4).

2. Signal Va21 is grounded via the transistor T32, the transistor T30 remains blocked and the capacitor C 19 can be charged by the current flowing through the transistor T31.

3. Once the capacitor C19 has been charged, the point n is at zero potential and the transistor T29 is blocked.

On completion of the action of pulse Va23, the transistors T28, T31 and T32 are again blocked and the circuit for forming the signal V9 remains in this state, with the capacitor C18 discharged and the capacitor C19 charged, until arrival of the next pulse of the signal Va21, one second after the first with which obviously no pulse of signal Va23 is associated, since the fre' quency of the latter is four times lower than that of signal Va21.

On the first pulse Va21 being supplied, following the pulse Va23, the following takes place:

1. The capacitor C19 is discharged.

2. The transistor T29 is unblocked, the potential at point 0 drops to Zero and the capacitor C18 is charged, so that the electrode of the capacitor C40 connected to the point 9, which had been maintained at the negative potential of the source P, is maintained at zero potential.

The alternating charging and discharging of the capacitors C18 and C19 has thus permitted the formation of a voltage pulse constituting the signal V9, of duration corresponding to the period of repetition of the pulses of signal Va21, in this case one second, the period of repetition of the signal V9 corresponding to that of the signal Va23, i.e., to 4 seconds in the example described.

A study will now be made of the manner in which there is effected detection of the position of the pivotable electrode 5 at the instant of the arrival of a pulse at point 9 of the circuit to which is connected one of the electrodes of the fixed capacitor C40, and how the correction device reacts to such detection.

For this purpose, it is necessary to distinguish with regard to the circuit of FIG. 2 the case of correct operation of the timepiece, from the case of lagging of the gear train of the timepiece.

CORRECT OPERATION At the instant of the simultaneous formation of the signals Va21 and Va23 which produce, every four seconds, the front of the pulse V9 (FIG. 4), as will be clear from the text hereinabove, the arms of the electrode 5 are spaced apart from the vanes 7a of the fixed armature and are in the position shown in broken lines (FIG. 1). As will be appreciated from the diagram of FIG. 5, the capacitive value of the detection capacitor C4 diminishes suddenly for an extremely small angular displacement 0: of its pivotable electrode 5.

In view of the fact that the capacitive value of the fixed capacitor C40 and the maximum capacitive value of the detection capacitor C4 are selected to be approximately equal, the sudden diminution in the capacitive value of the capacitor C4 will result in a substantial increase in the voltage at the point 10, at the instant at which thepulse front V9 is formed. The value of the voltage at point 10 is higher than the threshold voltage of the transistor -T27 and its duration is equal to that of the signal V9. Thus, during the entire duration of the pulse of signal V9, the transistor T27 is conductive and the pulses of signal Va20, which appear twice per second at the output a20 of the stage EC 20, are not able to reach the electrode controlling the transistor T25. The latter remains blocked, so that the pulse for correcting the signal Va20 which follows the pulse for normal entrainment of the signal Va2l does not contribute to the entrainment of the relay R6. I

Consequently, the pulses of signal Va2l and those of signal Vb20 normally feed the associated control electrodes of transistors T23 and T24 of the control circuit of theelectromechanical converter of the timepiece. The functioning of this circuit comprising the transistors T23, T24, T26 and of the capacitor C16 is described in British Pat. No. 1,177,523 to which reference should be made in order to have more details. We shall confine ourselves to recalling that it is the potential Vm at the point m in the said circuit which is decisive with regard to triggering of the transistor T26, which transistor permits passage of current through the coil R6 only when it is unblocked due to the appearance of the potential Vm at its control electrode.

LAG OF THE GEAR TRAIN The circuit shown in FIG. 2 is essentially intended to effect detection and correction of errors revealed in indication or display of the hour when the said errors involve a delay or lag. The circuit triggers, as to be described hereinbelow, the momentary connection of the entrainment circuit T23, T24, T25, T26, C16, R6 to the point a20 on the divider in such manner that, during the entire duration of such connection, the said circuit is triggered by a signal of double frequency relative to the signal issuing from point a21.

The circuit of FIG. 2 detects that there is a delay in operation of the gear train when the value of the capacity of the variable capacitor C4 is a maximum (this taking place when the arms are directly applied on the vanes 70) and when, simultaneously with this, the circuit receives the pulses of the signals Va2l and V1123.

In fact, since these signals originate the formation of the signal V9, the production of the signal V9 at the instant at which the capacitor C4 has a maximum value shows itself due to the appearance at the terminal of a potential of lower value than the threshold voltage of the transistor T27. Since the transistor 27 thus re mains blocked as long as the signal V9 persists, i.e., up to the voltage drop following the signal Va21, the pulse of the signal Va following the formation of the front of the signal V9 is able to reach the transistor control electrode T25, which opens.

As will be gathered from FIG. 2, the transistor T is connected in a manner equivalent to the transistor T24, i.e., in parallel with the capacitor C16, and so the transistor 25 is able to trigger discharge, of the capacitor C16, as is the transistor T24 when it becomes conductive.

It follows that, in respect of the entrainment circuit, the fact that the transistor T25 is conductive gives rise to the production of a pulse Vm, the result of this,

being as in the case of the pulses Vm already mentioned opening of the transistor T26 and, consequently, the passage of a driving pulse into the coil R6. Since the pulse Vm has been interposed between two pulse Vm, there has thus been effected the addition of a driving pulse to the normal train of pulses of frequency one cycle per second, whereby this supplementary pulse makes it possible to compensate for a second in time of the detected delay. It can thus be seen that the circuit components controlling the potential at point 10 constitute an error detector circuit coupled to capacitor C4, whilst the circuit components inserting extra pulse Vm constitute correcting means.

The circuit constituting the subject of FIG. 3 is essentially intended for the detection of possible advances in the operation of the timepiece and for the correction of such errors.

It is distinguished from that described with reference to FIG. 2, on the one hand by:

the addition of two elementary amplifiers to a transistor.

As can be seen in FIG. 3, amplifier T21, C14 is connected, at its input, to the point 10 in the circuit, and at its output to the electrode for controlling the transistor T22 and in parallel with the capacitors C4 and C40.

A further amplifier T22, C15 is connected at its output to the electrode for controlling or triggering the transistor T24 and is also connected to point 021 via its capacitorClS.

CORRECT OPERATION As in the case previously envisaged with regard to the detection of lag or delay, if the hour indication of the timepiece is correct, the pulse of the signal V9 is produced when the electrodes of the capacitor C4 are spaced apart and the capacity of the latter is particularly low (FIG. 5). It follows that the potential Vs at point 10, the value of which is defined by Vs (C40/C40 C4) V9 is then sufficiently high to produce the opening of transistor T21, the charging of capacitor C14, the mainte nance of transistor T22 in its non-conductive state, and thus the normal feeding of the coil R6 of the electromechanical converter due to the pulse Va2l.

ADVANCE OF THE GEAR TRAIN If the electrodes of the capacitor C4 occupy their closest position (shown in full lines in FIG. 1) at the instant at which the signal V9 is formed, indicating that the gear train is advanced, the potential at point 10 in FIG. 3 is lower than the threshold voltage of the transistor T21 which remains blocked. It is thus the transistor T22 which becomes conductive and consequently prevents the pulse of signal Va2l appearing across the outlet a2l of stage EC 21 from being applied to the control electrode of the transistor T24. The relay R6 is thus not actuated. There has thus been effected the suppression of a pulse Vm in the normal train of the driving pulses. It is necessary to point out that, due to the structural features of the capacitor C4, the detection of advance or delay previously referred to is particularly clear.

It can thus be seen that, in FIG. 3, the circuit components controlling the potential at point 10 constitute an error detector circuit coupled to capacitor C4, whilst the circuit components preventing the pulse of signal Va21 constitute correcting means.

In fact, and as will be more particularly clear from FIG. representing the variation in the capacity of the capacitor C4 as a function of the angular deviation of its electrodes, the said capacity varies very considerably for a very small spacing or deviation of the electrodes (of the order of a few degrees) from the closed position. Since, in FIGS. 2 and 3, capacitor C4 is connected in series with the capacitor C40, the capacity of which is substantially equal to the maximum capacity of the capacitor C4, it follows that, if the variation of the capacity of the latter is considerable, the potential Vs at the point is also modified to a considerable extent. The potential Vs corresponds, in fact, to the value defined by:

Vs (C40/C40 C4) V9 We should also point out, finally, that detection of advances and delays in the gear train position could readily be obtained by utilising two variable capacitors similar to the capacitor C4 and alternatingly actuated by the indicator gear train.

However, this solution would be relatively cumbersome and it would be perfectly possible to correct the advances and delays by means of the single detection device shown in FIG. 1. In order to correct both lag and advance, it would suffice to change over after each period of correction from the one to the other of two circuits such as those shown in FIGS. 2 and 3. If an error is detected, correction is effected up to disappearance of the error before changing over on to the other correction circuit.

I claim:

1. A timepiece indicator gear train having a rotatable element and means for sensing the angular position of said element, said means comprising:

relatively movable electrode surfaces which have a first relative position in which a movable one of said surfaces lies against another of said surfaces;

a dielectric layer provided on one of said electrode surfaces;

biasing means which urge said electrode surfaces to said first relative position;

a coupling portion of said gear train; and

a coupling portion of said one of said electrode surfaces for co-operation with said coupling portion of said gear train to cause said electrode surfaces to be periodically moved apart against the action of said biasing means during rotation of said element of said gear train.

2. A gear train as claimed in claim 1, wherein said biasing means are resilient biasing means.

3. A gear train as claimed in claim 1, wherein said coupling portion of said one of said electrode surfaces is an entrainment finger, said another of said electrode surfaces being fixed and said one electrode surface being movable relative to said another electrode surface by actuation of said entrainment finger.

4. A gear train as claimed in claim 1, wherein said rotatable element comprises at least one projection which is disposed eccentrically with respect to the axis of rotation of the rotatable element, said rotatable element being rotatable to periodicallyabut said coupling portion of said one electrodesurface thereby periodically to move said electrode surfaces apart against the action of said biasing means during rotation of said element.

5. A gear train as claimed in claim 1, wherein said another of said electrode surfaces is provided by a fixed member comprising a first plurality of vanes extending radially about an axis and said one of said electrode surfaces is provided by a pivotable member which is pivotable about said axis and which comprises a second plurality of vanes which extend between said first plurality of vanes such that said biasing means urge said second plurality of vanes into contact with said first plurality of vanes with interposition of said dielectric layer between said first and second pluralities of vanes. 6. A gear train as claimed in claim 1, wherein said surface upon which is provided said dielectric layer is of aluminium, and said dielectric layer itself comprises an oxide of aluminium.

7. An electronic timepiece comprising: a. a timepiece indicator gear train having a rotatable element and means for sensing the angular position of said element, said means comprising: relatively movable electrode surfaces which have a first relative position in which a movable one of said surfaces lies against another of said surfaces;

a dielectric layer provided on one of said surfaces;

biasing means which urge said electrode surfaces to said first relative position;

a coupling portion of said gear train; and

a coupling portion of said one of said electrode surfaces for co-operation with said coupling portion of said gear train to cause said electrode surfaces to be periodically moved apart against the action of said biasing mean during rotation of said element of said gear train;

b. electrically operable drive means coupled to said gear train;

c. a time base coupled to said drive means to operate said drive means in dependence upon periodic signals issued by said time base at a predetermined frequency; and

d. an error detector circuit coupled to said means for sensing the angular position of said element and also to said time base, said error detector circuit being operable to detect error in the angular position of said element in dependence upon a comparison between signals dependent upon said timebase and signals from said means for sensing the angular position of said element.

8. An electronic time piece as claimed in claim 7, including a source for issuing periodic signals at a submultiple of the frequency of, and in synchronism with, said time base; said source coupling the said time base to said drive means and to said error detector circuit.

9. An electronic time piece as claimed in claim 8, wherein said source is constituted by at least one frequency demultiplierv stage.

10. An electronic time piece as claimed in claim 7, wherein said biasing means are resilient biasing means.

11. An electronic time piece as claimed in claim 7, wherein said coupling portion of said one of said electrode surfaces is an entrainment finger, said another of said electrode surfaces being fixed and said one electrode surface being movable relative to said another electrode surface by actuation of said entrainment finger.

12. An electronic time piece as claimed in claim 7, wherein said rotatable element comprises at least one projection which is disposed eccentrically with respect to the axis of rotation of the rotatable element, said rotatable element being rotatable to periodically abut said coupling portion of said one electrode surface thereby periodically to move said electrode surfaces apart against the action of said biasing means during rotation of said element.

13. An electronic time piece as claimed in claim 7, wherein said another of said electrode surfaces is provided by a fixed member comprising a first plurality of vanes extending radially about an axis and said one of said electrode surfaces is provided by a pivotable member which is pivotable about said axis and which comprises a second plurality of vanes which extend between said first plurality of vanes such that said biasing means urge said second plurality of vanes into contact with said first plurality of vanes with interposition of said dielectric layer between said first and second pluralities of vanes.

14. An electronic time piece as claimed in claim 7, including correcting means for correcting any error detected by said error detector circuit.

15. An electronic time piece as claimed in claim 14, wherein said correcting means includes means for preventing periodic drive signals being fed to said drive means in the event that said error is an advance.

16. An electronic timepiece as claimed in claim 14, wherein said correcting means includes means for feeding additional periodic drive signals to said drive means in the event that said error is a lag.

17. An electronic time piece as claimed in claim 7, wherein said surface upon which is provided said dielectric layer is of aluminium, and said dielectric layer itself comprises an oxide of aluminium. 

1. A timepiece indicator gear train having a rotatable element and means for sensing the angular position of said element, said means comprising: relatively movable electrode surfaces which have a first relative position in which a movable one of said surfaces lies against another of said surfaces; a dielectric layer provided on one of said electrode surfaces; biasing means which urge said electrode surfaces to said first relative position; a coupling portion of said gear train; and a coupling portion of said one of said electrode surfaces for co-operation with said coupling portion of said gear train to cause said electrode surfaces to be periodically moved apart against the action of said biasing means during rotation of said element of said gear train.
 2. A gear train as claimed in claim 1, wherein said biasing means are resilient biasing means.
 3. A gear train as claimed in claim 1, wherein said coupling portion of said one of said electrode surfaces is an entrainment finger, said another of said electrode surfaces being fixed and said one electrode surface being movable relative to said another electrode surface by actuation of said entrainment finger.
 4. A gear train as claimed in claim 1, wherein said rotatable element comprises at least one projection which is disposed eccentrically with respect to the axis of rotation of the rotatable element, said rotatable element being rotatable to periodically abut said coupling portion of said one electrode surface thereby periodicAlly to move said electrode surfaces apart against the action of said biasing means during rotation of said element.
 5. A gear train as claimed in claim 1, wherein said another of said electrode surfaces is provided by a fixed member comprising a first plurality of vanes extending radially about an axis and said one of said electrode surfaces is provided by a pivotable member which is pivotable about said axis and which comprises a second plurality of vanes which extend between said first plurality of vanes such that said biasing means urge said second plurality of vanes into contact with said first plurality of vanes with interposition of said dielectric layer between said first and second pluralities of vanes.
 6. A gear train as claimed in claim 1, wherein said surface upon which is provided said dielectric layer is of aluminium, and said dielectric layer itself comprises an oxide of aluminium.
 7. An electronic timepiece comprising: a. a timepiece indicator gear train having a rotatable element and means for sensing the angular position of said element, said means comprising: relatively movable electrode surfaces which have a first relative position in which a movable one of said surfaces lies against another of said surfaces; a dielectric layer provided on one of said surfaces; biasing means which urge said electrode surfaces to said first relative position; a coupling portion of said gear train; and a coupling portion of said one of said electrode surfaces for co-operation with said coupling portion of said gear train to cause said electrode surfaces to be periodically moved apart against the action of said biasing mean during rotation of said element of said gear train; b. electrically operable drive means coupled to said gear train; c. a time base coupled to said drive means to operate said drive means in dependence upon periodic signals issued by said time base at a predetermined frequency; and d. an error detector circuit coupled to said means for sensing the angular position of said element and also to said time base, said error detector circuit being operable to detect error in the angular position of said element in dependence upon a comparison between signals dependent upon said timebase and signals from said means for sensing the angular position of said element.
 8. An electronic time piece as claimed in claim 7, including a source for issuing periodic signals at a sub-multiple of the frequency of, and in synchronism with, said time base; said source coupling the said time base to said drive means and to said error detector circuit.
 9. An electronic time piece as claimed in claim 8, wherein said source is constituted by at least one frequency demultiplier stage.
 10. An electronic time piece as claimed in claim 7, wherein said biasing means are resilient biasing means.
 11. An electronic time piece as claimed in claim 7, wherein said coupling portion of said one of said electrode surfaces is an entrainment finger, said another of said electrode surfaces being fixed and said one electrode surface being movable relative to said another electrode surface by actuation of said entrainment finger.
 12. An electronic time piece as claimed in claim 7, wherein said rotatable element comprises at least one projection which is disposed eccentrically with respect to the axis of rotation of the rotatable element, said rotatable element being rotatable to periodically abut said coupling portion of said one electrode surface thereby periodically to move said electrode surfaces apart against the action of said biasing means during rotation of said element.
 13. An electronic time piece as claimed in claim 7, wherein said another of said electrode surfaces is provided by a fixed member comprising a first plurality of vanes extending radially about an axis and said one of said electrode surfaces is provided by a pivotable member which is pivotable about said axis and which comprises a second plurality of vanes whIch extend between said first plurality of vanes such that said biasing means urge said second plurality of vanes into contact with said first plurality of vanes with interposition of said dielectric layer between said first and second pluralities of vanes.
 14. An electronic time piece as claimed in claim 7, including correcting means for correcting any error detected by said error detector circuit.
 15. An electronic time piece as claimed in claim 14, wherein said correcting means includes means for preventing periodic drive signals being fed to said drive means in the event that said error is an advance.
 16. An electronic timepiece as claimed in claim 14, wherein said correcting means includes means for feeding additional periodic drive signals to said drive means in the event that said error is a lag.
 17. An electronic time piece as claimed in claim 7, wherein said surface upon which is provided said dielectric layer is of aluminium, and said dielectric layer itself comprises an oxide of aluminium. 